MAN B & W DIESEL A/S has recently developed a new type of fuel injection valves named “slide fuel valves” of the types K 90 MC-C and K 80 MC-C, etc, confer FIG. 2. Compared to conventional valves, confer FIG. 1, a void in the valve tip called the “sac volume” or clearance volume has been eliminated, thereby preventing an untimely injection of a small volume of fuel corresponding to the clearance volume (typically 1-2 cm3). This has resulted in a reduced sooting of the diesel engine, reduced smoke generation, lower NOx and VOC emissions and not least improved fuel efficiency.
The fuel injection valve should be checked on a regular basis inter alia to ensure that inter alia the opening pressure is correct. The opening pressure may for instance have changed due to slackness in a built-in spring in the valve. Furthermore the venting pressure is checked and a “carburetion test” may also be carried out. The conventional equipment for checking fuel valves, including the opening pressure, the venting pressure, and the carburetion test operates in the following manner. Compressed air (5-10 bar) is supplied to a pneumatic pump, which converts the air pressure to a hydraulic oil pressure of several hundred bar. All tests are performed by feeding pure test oil to the valve at specific pressures, whereby it is possible to test that the various parts of the valve function correctly. At the opening pressure test the pressure in the valve is gradually increased until a built-in slide body in the valve is activated and the valve is opened briefly, whereafter the pressure drops slightly and the slide body recloses until the pressure once again exceeds the opening pressure. In the carburetion test an internal oil pressure is generated in the pump, said pressure exceeding the opening pressure of the valve considerably. When the connection between the pump and the injection valve is established, usually by pulling a large lever, confer FIG. 7, the valve immediately begins to rattle until the connection between the injection valve and the pump is cut off. This conventional test equipment has, however, a disadvantageous influence on the functionality of the new valves. The new valves with a built-in slide body in the valve tip do not tolerate being subjected to the conventional carburetion test and they are subjected to unnecessary stress by being subjected to the normal opening test with several successive openings. The reason why the valves with slide bodies break when the carburetion test (and/or a too thorough execution of the opening pressure test) is performed is presumably that defects arise on the valves due to the differing physico-chemical properties of the test oil and of the normal diesel oil. In addition hereto, metals expand when heated. Other things being equal, the outer face of the valve tip is hotter than the metallic slide body situated inside the valve, which means that the friction resistance therebetween is higher during testing than during normal operation.